A process for forming a photoresist pattern is disclosed. In particular, a process for forming a photoresist pattern is disclosed that comprises the steps of treating an exposed photoresist resin with a basic gas phase compound under conditions sufficient to form a substantially vertical pattern.
Current methods allow production of 150 nm L/S photoresist patterns using 248 nm wavelength light (e.g., KrF exposer). However, formation of high quality photoresist patterns smaller than 150 nm L/S have been relatively unsuccessful. For example, use of short wavelength light sources, such as ArF (193 nm), F2 (157 nm), EBW (13 nm), with low transmittance photoresist resins have resulted in poor quality patterns. And photoresist resins that are typically used with i-line (365 nm) and KrF (248 nr) light sources have a relatively high absorbance of 193 nm wavelength light because they typically contain aromatic compounds. Therefore photoresist resins comprising aromatic compounds are not suitable to use with ArF light source. Photoresist compositions comprising acrylic or alicyclic resins developed for ArF light source still have a relatively high absorbance of 193 nm wavelength light even though they contain no aromatic compounds. In addition, 157 nm L/S photoresist patterns produced from photoresist resins comprising typical organic compounds are generally of a poor quality because Cxe2x80x94H, Cxe2x95x90C, Cxe2x95x90O bonds and aromatic compounds readily absorb 157 nm wavelength light.
Use of conventional chemically amplified photoresist resins having a low transmittance result in majority of light absorption in the upper portion of the photoresist resin and a significantly lower amount of light reaching the bottom portion of the photoresist resin. Thus, a higher amount of acid is generated in the upper portion of the photoresist resin compared to the lower portion of the photoresist resin. This acid gradient can result in a bulk slope profile pattern as shown in FIG. 1b. 
One method of overcoming some of the above described problems is to use a photoresist resin which has a relatively high transmittance. Using a high transmittance photoresist resin results in a substantially equal amount of light reaching both the upper and bottom portions of the photoresist resin, which allows formation of a desired vertical pattern as shown in FIG. 1a. While efforts have been made to produce a fine photoresist pattern (i.e., 150 nm L/S or better) using a photoresist resin and light wavelengths of 157 nm (F2) and 13 nm (EUV), these efforts have not been successful thus far.
A process for forming a substantially vertical photoresist pattern is disclosed even when a highly light absorbing (i.e., low transmittance) photoresist resin is used.